Generally there is(are) a main power breaker(s) inside the box, typically very near the top; could be two depending on the size of your service ( 110 vs 220 and the total number of number of circuits.) I wouldn't be surprised if #17 has only one hot wire to the breaker and one ground (white) to the box lugs that is sometimes across the bottom or vertically between the 2 rows of breakers, also all inside, under the cover you haven't take off yet. That would mean that more than one room is on a single circuit.
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